1. Field of the Invention
The present invention relates in general to the field of hologram production and, more particularly, to production of updateable holograms.
2. Description of the Related Art
One-step hologram (including holographic stereogram) production technology has been used to satisfactorily record holograms in holographic recording materials without the traditional step of creating preliminary holograms. Both computer image holograms and non-computer image holograms can be produced by such one-step technology. In some one-step systems, computer processed images of objects or computer models of objects allow the respective system to build a hologram from a number of contiguous, small, elemental pieces known as elemental holograms or hogels. To record each hogel on holographic recording material, an object beam is typically directed through a spatial light modulator (SLM) displaying a rendered image and then interfered with a reference beam. Examples of techniques for one-step hologram production can be found in the U.S. Pat. No. 6,330,088 entitled “Method and Apparatus for Recording One-Step, Full-Color, Full-Parallax, Holographic Stereograms,” naming Michael A. Klug, Mark E. Holzbach, and Alejandro J. Ferdman as inventors, (“the '088 patent”) which is hereby incorporated by reference herein in its entirety.
In general, the techniques described in the '088 patent and other prior art techniques do not provide for both hologram recording and display in real-time. Moreover, these techniques are not designed to produce active or quickly-updateable displays. There are significant applications for a display that is capable of producing autostereoscopic holographic three-dimensional images that are interactive and update-able in a reasonable amount of time (e.g., on the order of seconds or minutes). However, there are three significant obstacles to producing such a display: (1) selecting a suitable display medium capable of recording, displaying, erasing or replacing, and updating the image; (2) communications bandwidth necessary to transfer the enormous amounts of data necessary to produce an image on the display; and (3) rendering hardware and software that is fast enough to produce a real-time or quasi-real time, interactive experience.
There have been a number of efforts to develop a real-time holographic display, most notably by Steve Benton's Spatial Imaging Group at the MIT Media Laboratory, and by a group at QinetiQ, a spin-off company from the UK's Defense Evaluation and Research Agency (DERA). These efforts have produced some promising but limited results.
The MIT effort resulted in a monochrome display with dimensions of approximately 75 mm×100 mm, and exhibiting horizontal parallax only. The system is based on first computing fringe patterns using physical simulation, displaying them piecewise in an acousto-optic modulator (AOM), and then raster scanning a demagnified image of the AOM to produce a larger display. Images produced on the MIT display have approximately 30 degrees of horizontal viewzone, and the vertical resolution is limited to 144 lines. Many of the image quality tradeoffs of the MIT system reflect a need to minimize the total data bandwidth of the system. As a result, each frame of the display contains approximately 36 megabytes of information. Custom and customized hardware enable the display to be updated at up to 2 to 3 frames per second with pre-stored image information. Since the system requires complex computational physical simulation to produce holographic fringe patterns, real-time updating is difficult.
The QinetiQ approach also relies on physical simulation to produce synthetic fringe patterns. These, however, are written onto an electrically-addressed spatial light modulator (EASLM), and are demagnified and re-imaged onto an optically-addressed spatial light modulator (OASLM) for final display. The approach is potentially capable of producing full-parallax images, and is scalable through tiling multiple EASLM/OASLM units together. The system has not been publicly demonstrated to date, and thus it is difficult to assess its characteristics and effectiveness. Computational elements of the QinetiQ display have been documented, but the performance of the system has not been demonstrated.
Both the MIT and QinetiQ approaches rely on complex physical simulation to calculate holographic fringe patterns which are then downloaded to the display hardware. Light being directed through that hardware diffracts from these fringes, and reproduces wavefronts, or approximations thereof, of the desired imaged object or scene. This approach has limitations because it relies on the need for a display device with extremely high resolution that can be electronically addressed in order to enable writing of the fringe pattern. Such approaches often have limited resolution, and rely on demagnification to achieve the high resolution necessary to diffract light. Limited space-bandwidth products of such approaches in turn limit the viewing angle and resolution of the final image.
Accordingly, it is desirable to have improved systems and methods for producing updateable or active hologram displays that avoid the need for complex physical simulation to produce synthetic fringe patterns. Moreover, it is desirable that such systems and methods high resolution images that possess adequate field of view properties.